Possible origins of anomalous H I gas around MHONGOOSE galaxy, NGC 5068^⋆

¹ Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
e-mail: juliahealyza@gmail.com
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
³ Department of Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa
⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁵ Aix-Marseille Univ., CNRS, CNES, LAM, 38 Rue Frédéric Joliot Curie, 13338 Marseille, France
⁶ Instituto de Astrofísica, Facultad de Ciencias Exactas, Universidad Andrés Bello, Chile
⁷ LERMA, Observatoire de Paris, PSL Research Université, CNRS, Sorbonne Université, 75104 Paris, France
⁸ Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
⁹ University of Louisville, Department of Physics and Astronomy, 102 Natural Science Building, Louisville, 40292 KY, USA
¹⁰ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
¹¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹² Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Station Forces Kingston, ON K7K 7B4, Canada
¹³ Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, ON K7L 3N6, Canada
¹⁴ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain
¹⁵ Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
¹⁶ Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
¹⁷ Département de physique, Université de Montréal, Complexe des sciences MIL, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, QC H2V 0B3, Canada
¹⁸ Laboratoire de Physique et de Chimie de l’Environnement, Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo (ODAUO), BP 7021, Ouaga 03, Burkina Faso

Received: 14 July 2023
Accepted: 12 February 2024

Abstract

The existing reservoirs of neutral atomic hydrogen gas (H I) in galaxies are insufficient to have maintained the observed levels of star formation without some kind of replenishment. This refuelling of the H I reservoirs is likely to occur at column densities an order of magnitude lower than previous observational limits (N_{H I, limit} ∼ 10¹⁹ cm⁻² at a 30″ resolution over a linewidth of 20 km s⁻¹). In this paper, we present recent deep H I observations of NGC 5068, a nearby isolated star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. With these new data, we were able to detect low column density H I around NGC 5068 with a 3σ detection limit of N_H I = 6.4 × 10¹⁷ cm⁻² at a 90″ resolution over a 20 km s⁻¹ linewidth. The high sensitivity and resolution of the MeerKAT data reveal a complex morphology of the H I in this galaxy – a regularly rotating inner disk coincident with the main star-forming disk of the galaxy, a warped outer disk of low column density gas (N_H I < 9 × 10¹⁹ cm⁻²), in addition to clumps of gas on the north-western side of the galaxy. We employed a simple two disk model that described the inner and outer disks, which enabled us to identify anomalous gas that deviates from the rotation of the main galaxy. The morphology and the kinematics of the anomalous gas suggest a possible extra-galactic origin. We explore a number of possible origin scenarios that may explain the anomalous gas, and conclude that fresh accretion is the most likely scenario.